The present invention relates to a lens system in which in a copying system such as a large size copying camera or duplicating camera, the distance between the objective suface and the film surface is maintained constant and the overall lens system is moved therebetween to thereby carry out variable magnification copying. In such a copying lens system, it is particularly necessary to compensate for various aberrations and to provide a sufficient quantity of marginal light.
Prior art copying lens systems may be classified into two groups, a first group having a wide range of magnification extending from a reduced size to a enlarged size and a second having a narrow range of magnification extending only from the reduced size to the size of the original or from the size of the original to the enlarged size. A lens system of the first group is disclosed in unexamined Japanese Patent Publication Nos. 49/1242 and 53/60655 and Japanese Patent Application No. 53/84872 which are assigned to the assignee of the present application. In these lens systems, the magnification variation ratio is high resulting in the lens system having a large physical size. Such a lens system moreover requires three or four separate lens groups with the result that the movements of the lens groups are intricate for maintaining constant the distance between the object surface and the film surface.
Lens systems of the second group are disclosed in unexamined Japanese Patent Publication No. 54/44554 and Japanese Patent Publication No. 54/77925 which was filed by the present application. The lens disclosed therein is of type having an asymmetrical construction. Therefore, its power variation and performance are limited to a certain level.